1. Field of the Invention The present invention relates to method and apparatus for measuring traffic flow by detecting the presence of a vehicle, the type of vehicle and the individual vehicle velocity from an image information picked up by an ITV (industrial television ) camera.
The type of vehicle in the present specification means a classification of car size such as a small size car and a big size car, unless otherwise specified.
2. Related Background Art
In a traffic control system for a public road and a highway, a number of vehicle sensors are arranged to measure traffic flow. One advanced system for such measurement is a traffic flow measurement system by an ITV camera.
The above traffic flow measurement system uses the ITV camera as a sensor. Specifically, it real-time analyzes image information derived by the ITV camera which obliquely looks down a road to determine the presence of a vehicle and a velocity thereof.
FIG. 1 illustrates an outline of a prior art traffic flow measurement system. FIG. 1A shows a measurement area 51 displayed on an image screen of the ITV camera. FIG. 1B shows measurement sampling points set for each lane in the measurement area 51. FIG. 1C shows a bit pattern of measurement sampling points transformed from the measurement sampling points in the measurement area 51 to orthogonal coordinates and a vehicle region (represented by code level "1"). FIG. 1D shows a bit pattern of a logical OR of the elements along a crossing direction of the road (The vehicle region is represented by the code level "1").
The detection of the vehicle region, that is, a process for imparting a code level "0" or "1" to each measurement sampling point is effected by calculating a difference between brightness data of each measurement sampling point and road reference brightness data and binarizing the difference.
Traffic amount, velocity, type of vehicle and the number of vehicles present can be determined based on a change in the detected vehicle region (represented by the code level "1"). (See SUMITOMO ELECTRIC, No. 127, pages 58-62, September 1985.) The algorithm of the traffic flow measuring method in the prior art traffic flow measurement system described above has the following problems. First, since the road brightness is to be changed depending on time of day such as morning or evening and as a result of weather, a manner of setting the road reference brightness data is complex.
Specifically, in the evening, a detection precision is low because a difference between the brightnesses of a car body and the road is small. At night, since head lights are subject to be recognized, a detection rate for a car which lights only low brightness small lamps (lights to indicate a car width) decreases.
Secondly, since the bit pattern of the measurement area (FIG. 1C) viewed along the crossing direction of the road (logical OR of the elements along the crossing direction) is determined and the vehicle region is determined based on the bit pattern as shown in FIG. 1D, the measurement area must be divided for each lane. A new problem arising from this method is that a vehicle which runs across the lane is counted as two vehicles.
Thirdly, a non-running car or parked car is recognized as the road when it is compared with the road reference brightness data, and the presence of such car is not detected.